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26 • ROCK products • May 2016 www.rockproducts.com This has worked well on many large, sensitive projects, in- cluding one in Grundy, Va. (Figure 4). In this blast there were four different rock types that varied throughout the face and a straight highwall had to be maintained. This increased flexibility in precision presplitting allowed for more control over the final wall at a mining operation. Another feature of a precision presplit is that it's bot- tom-primed with either a cast booster or a cap-sensitive chub of emulsion or dynamite. While this does add a little extra power to the bottom of the blast, the main benefit is the extra weight it gives on the detonating cord. This makes the blast much easier and quicker to load. While precision presplitting uses much less explosives, it generally increases the total drilling because of a reduction of the spacing. Looking at design variables and the economic variables one can analyze the differences between the two methods of presplitting. Once an economic consideration is placed on the benefit of having a smoother wall, a mine can then make an evaluation of whether precision presplitting is worth the investment. In the table below a comparison of these two forms of presplitting is done. Parameter Traditional Presplit Precision Presplit Bench Height (ft.) 35 35 Drillhole Diameter (in.) 3 3 Spacing (in.) 36 24 Powder Load (lb. per ft.) 0.32 0.08 Stemming (in.) 36 30 Timing Instant Instant/delay Lb. per sq. ft. 0.12 0.05 Drilling per sq. ft. 0.33 0.50 For instance, if a quarry had a drilling cost of $3 per linear ft. and similar cost per lb. of explosives of $3 per lb. In this case the quarry would reduce the explosive cost of their presplit by $0.21 per sq. ft.. At the same time, their total drilling cost per sq. ft. would increase by $0.51. Therefore, the quarry would increase the cost of presplitting by $0.30 per sq. ft. Little if any scaling of the final wall would be required. Next the quarry needs to determine the monetary gain by receiving a smooth wall. If this quarry spends $50,000 per year in scaling and berms to improve their safety near the face and has a total of 3,000 ft. of a highwall (which is 35-ft. high), this is a total savings of $0.48 per sq. ft. In the end, by switching to precision presplitting this mine would save $0.18 per sq. ft. for a total of $18,900. The current methods of presplitting used in the mining and construction industry today are extremely ineffective when weaker or geologically unique rock is being presplit. Unfor- tunately, a presplit is normally necessary in a weaker rock to increase safety and prevent overbreak of the face. The new form of precision presplitting is designed specifi- cally to form a smooth crack to the top of the highwall in all rock types. Precision presplitting has now been proven to work on many projects such as the Folsom Dam, Kentucky Locks, Panama Canal, etc., and is being used in the mining industry today to increase safety and prevent overbreak in weaker rocks. In the next issue we will discuss how to calculate the explo- sive loads for a precision presplit based on the rock types and characteristics. Dr. Calvin Konya is the president of Precision Blasting Services, and Anthony Konya is a project engineer for the company. Figure 4 - Grundy, Va. PRESPLITTING